1. Field
This invention relates to compound archery bows. It is particularly directed to an improved pulley assembly for such bows.
2. State of the Art
Compound archery bows commonly carry assemblies of pulley members (usually called “eccentrics” or “cams”) eccentrically mounted on axles in association with respective bow limbs. These limbs extend in opposite directions from a grip (usually comprising a central portion of a handle riser). The rigging for compound bows includes a bowstring trained around the pulley members of the system, the string being received by grooves or other functionally equivalent features at the perimeters of the pulleys. The eccentric pulley assemblies are conventionally mounted to rotate (pivot) on an axle within a notch at the distal end of the limb, or within a bracket structure carried by the limb tip. The eccentrics include one or more pivot holes substantially offset from center, whereby to provide for a reduction in the holding force felt at the nocking point of the bowstring, as the string is moved to its fully drawn condition.
Compound bows and various exemplary riggings, including pulley assemblies, are described by U.S. Pat. Nos. 3,486,495; 3,990,425; 4,748,962; 4,774,927; 4,967,721; 6,763,818; and 7,441,555 the disclosures of which are incorporated as a portion of this disclosure.
The rigging for compound bows typically includes cable segments, which may be end stretches extending from an integral bowstring. More often, however, the cable segments are separate elements, each connecting at one end, directly or indirectly, e.g., through structure associated with the pulley assembly, to a terminal end of the bowstring. The remaining (distal) ends of the cable segments are conventionally connected to the opposite bow limb or structure, such as the pivot axle mount of the pulley assembly carried by that limb. In any case, each cable segment includes one or two stretches oriented approximately parallel the bowstring.
“Approximately parallel,” is intentionally fluid in context, merely recognizing that the cable segments and bowstring all extend generally across, but out of contact with, the handle riser portion of the bow between the pulley assemblies, or other structure, carried by the respective bow limbs. All of the cable stretches are thus confined within a space defined by reference planes straddling the handle riser and containing the bowstring. The cable stretches are commonly positioned to one side of the bowstring to avoid interference with the nocking point of the bowstring. It is common practice to mount cable guard rods or other structures to the handle riser. These structures are positioned physically to hold the cables away from the plane of travel of the bowstring. Compound bows have sometimes been configured to position cables on opposite sides of a bowstring so that an arrow may be cast in the plane of the bowstring between cable stretches.
With a compound bow oriented in its normal position of use, it is conventional to consider the bow as being oriented vertically. Unless otherwise stated, the bows referred to in this disclosure are assumed to be in this “vertical” orientation. The handle riser is thus considered to have an “upper end,” a “lower end” and a central grip portion. The limb extending from the upper end of the handle riser may be referred to as “a first limb” or the “upper limb,” in either case terminating in an “upper limb tip.” Corresponding terminology is applied to the “second limb,” which extends from the lower end of the handle riser. The bowstring is assumed to travel in a plane (“operating plane”) of travel between a fully drawn condition and braced or at rest condition. Cable stretches may be viewed as being positioned to the left or right of the plane of travel of the bowstring, recognizing that in some rigging systems, a cable stretch may be to one side of that plane of travel along the first limb and to the opposite side of that plane of travel as the stretch proceeds to its point of attachment at the second limb.
Proper operation of a compound bow typically requires periodic “tuning;” that is, synchronization of the pulley members. The pulley assemblies must be synchronized in their rotation so that the mechanical advantages developed through the two assemblies change at the same rate and to the same degree. Over a period of use, for various reasons, including stretching of the bowstring, compound bows typically migrate out of tuned condition. Re-tuning of the bow requires time consuming and technically demanding adjustments of the rigging. A number of efforts have been made to modify the rigging of compound bows to overcome or reduce the tuning requirement of such bows. These efforts have had little practical success. The persistent need for tuning and re-tuning is believed to be a major impetus for the wide acceptance of single cam bows. Single cam bows are believed by most archers to require much less effort to keep in tune, although the performance of the single cam configuration is less desirable in other respects than is the performance of conventional compound bows.
U.S. Pat. Nos. 3,990,425 and 6,990,870 propose rigging systems that cross-couple the pulley assembles of a compound bow so that they are constrained to move in unison, thereby providing a self-tuning function to the bow. The term “cross-couple” (sometimes “cross-coupling,” or “cross-coupled”) designates a rigging in which the cable end conventionally attached to the pulley axles are instead attached to a synchronizing sheave of the pulley assembly. To the extent that this expedient has been incorporated into commercial compound bows, the riggings have tended to exacerbate the inherent characteristic of pulley assemblies to twist (or lean) on their axle mounts. The riggings employed to date in cross-coupled bows apply cable force to the limb tips in a fashion that imparts a twisting moment to the mounting axles of the pulley assemblies. The '425 patent discloses pulley assemblies in which cross-coupling is accomplished through an anchoring arrangement that inherently imparts a leaning moment to the pulley assemblies. Specifically, the cables are all disposed to one side of the bowstring. The '870 patent disclosure includes riggings configured to apply cable forces more evenly, thereby reducing the twisting moment applied to the axle of the assembly. Moreover, the '870 patent discloses cross-coupled pulley assemblies within the riggings of single cam compound bows.
Commonly assigned, copending patent application Ser. No. 11/241,030, filed Sep. 30, 2005, the disclosure of which is incorporated by reference, also discloses several alternative embodiments of cross-coupled compound bows.
The conventional practice in constructing compound bows has been to mount all pulley components onto stationary axles. Originally, the pulleys were provided with bushings, rotatably mounted on an axle. More recently, these bushings have been replaced with bearing assemblies of various kinds, Exemplary bearing arrangements for compound bow are described and illustrated by U.S. Pat. No. 6,415,780.
The pulley assemblies in common use currently are typically machined, or otherwise formed, from a common block of material. In some instances pulley components are connected together with pins, bolts or screws. In any case, all of the pulley members of the assembly form a unitary structure mounted to turn upon an axle. The axle may be clamped or otherwise fixed with respect to a limb tip of the bow. In practice, however, operation of the bow is not negatively impacted by minor rotation of the axle with respect to the limb tip, provided the assembly is free to turn upon the axle.
Historically, excessive limb breakage has been associated with the construction practice of positioning an axle directly through channels transverse and within a limb tip of a bow. This problem has been partially alleviated in some constructions by mounting the pulley assembly in a bracket fixed to a limb tip. The use of brackets for this purpose is thought to impact negatively upon bow performance because of the added bracket weight carried by the limb tip under dynamic conditions.
A primary consideration in the design of cam assemblies for a compound bow is the relative configurations of the working portions of the string and cable grooves, respectively. The relationship of these working portions under dynamic conditions has a direct impact upon both the force-draw curve experienced by the archer and the shooting characteristics of the bow upon release of an arrow from drawn condition. It is general practice to wind the strings and cables, respectively, of a rigging such that the tension of the bowstring is opposed by the tension in the cables. During the draw portion of a shooting cycle, the torque applied to a pulley assembly, via the string groove, by the string increases substantially. The opposing torque simultaneously applied by a cable, via a cable groove, to the assembly also increases substantially. These opposing torques are resisted by the relatively massive cross section of the pulley assembly, and are isolated from the pivot axle.